The purpose or this protocol is to produce, isolate, purify, and characterize a newly discovered, lymphocyte derived prolactin-like growth factor. Preliminary experiments have demonstrated that human tumor infiltrating lymphocytes (TIL) produce small quantities of a growth factor that is detectable only when they are expanded to massive numbers within CELLMAX hollow fiber cell culture systems. This factor stimulates not only TIL growth but also that of other lymphoid and epithelial cell lines in vitro. Additional studies have shown that this factor is, or is associated with, one or mare of a family of several components that were identified by and then inactivated by antibodies directed against human prolactin. The present program proposes to produce this growth factor from TIL cultured from the tumors of 5 patients sufficient quantity to the permit its isolation and our purification and then determine its mode of interaction with cells of the immune system and other epithelial cells of both neoplastic and non-neoplastic origin. This would have important implications in the production of immune-competent lymphocytes for the adoptive immunotherapy of cancer and other autoimmune diseases.